Tuesday, 24 March 2009

A popular account for how we empathise with other people's physical pain involves the idea that we perform a mental simulation of their suffering, using the pain pathways of our own brain. Support for this comes from research showing that when I see you in pain, the pain areas of my own brain are pricked into activity.

Now an intriguing study by Nicolas Danziger and colleagues has tested this simulation account with the help of patients with congenital insensitivity to pain - that is, they've grown up with abnormal pain fibres, thus rendering them unable to feel physical pain. The findings may require us to rethink the way we characterise some brain areas associated with pain processing.

Thirteen patients with the inability to feel pain, plus 13 healthy controls, had their brains scanned while they viewed videos of body parts being injured and people's painful facial expressions.

Even though the patients had never felt pain themselves, the sight of other people's pain triggered activity in the insular and anterior mid-cingulate cortex of their brains - areas which have previously been associated with pain processing, and which were also activated in the brains of the controls.

"These findings challenge the frequently advanced hypothesis that activity in these regions during observed pain corresponds to the automatic engagement of the observer's own pain circuits through a mirror matching mechanism," the researchers said.

Danziger's team argue that activity in these regions may instead reflect processing of the aversive emotional significance of what the patients were witnessing. Consistent with this account are findings showing that the insular and mid-cingulate cortex are also associated with psychological pain, induced by social exclusion or grief. Perhaps the patients in this study drew on their experience of this kind of pain so as to empathise with the physical pain of others.

This fits with the fact that the control participants, but not the patients, showed more physical arousal when their insular and mid-cingulate cortex were more active, whereas the patients did not. The implication being that the control participants were simulating the pain seen in the clips in a more "embodied" way than the patients.

A further finding was that for the patients only, their scores on an empathy questionnaire correlated with the extent to which the pain-related video clips triggered activity in midline brain regions known to be involved with taking the perspective of others (e.g. the medial pre-frontal cortex). Danziger and his colleagues said this could further reflect the fact that the patients were relying on emotional perspective taking to compensate for their inability to simulate the sensory aspects of pain.
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